code: def test_constituency_parser(self):
      nlp = stanza.Pipeline(
          dir=TEST_MODELS_DIR, processors="tokenize,pos,constituency"
      )
      doc = nlp("This is a test")
      assert (
          str(doc.sentences[0].constituency)
          == "(ROOT (S (NP (DT This)) (VP (VBZ is) (NP (DT a) (NN test)))))"
      )
  
imports: import pytest
  import stanza
  from stanza.utils.conll import CoNLL
  from stanza.models.common.doc import Document
  from stanza.tests import *
  from stanza.tests.pipeline.pipeline_device_tests import check_on_gpu, check_on_cpu
label_desc: Use image node_id 20 for calling the TestEnglishPipeline obj's underlying member method code with example usage: obj.test_constituency_parser() without return types